OLYMPIA, Wash., Feb 28 (Reuters) - Nearly 25 years after the Exxon Valdez oil spill off the southern coast of Alaska, sea otters in the most affected parts of Prince William Sound have recovered to their pre-spill numbers, a federal report released on Friday showed.
Several thousand sea otters died in the aftermath of the oil tanker running aground on Bligh Reef and leaking 42 million liters of crude oil into the sound in March 1989, according to the U.S. Geological Survey, which issued the report.
The report's findings underscore the lengthy recovery times for many species affected by oil spills, U.S. Geological Survey research biologist Brenda Ballachey said in a statement.
"Although recovery timelines varied widely among species, our work shows that recovery of species vulnerable to long-term effects of oil spills can take decades," said Ballachey, the study's lead author.
Scientists assessed the otters' recovery by using aerial surveys, measuring oil exposure as indicated through gene expression and by evaluating the animals after death.
After the spill, middle-aged otters died at a higher-than-normal rate - a trend that has since reverted to the pre-spill pattern of most otters dying either very old or very young, the study found.
The slow pace of recovery for the otters was likely due to their ongoing exposure to oil, the study found.
Sea otters were among more than 20 near-shore animal species damaged by the spill, the U.S. Geological Survey said. (Reporting by Jonathan Kaminsky; Editing by Dan Whitcomb and Ken Wills)